The present invention relates to a cylinder head gasket situated between a cylinder head and a cylinder block in an internal combustion engine to seal therebetween.
More particularly, the present invention relates to a metal cylinder head gasket provided with a grommet, in which the grommet and base plates are formed of different materials so that the cylinder head gasket has a high sealing ability and an excellent durability.
In case of sealing joining surfaces of a cylinder head and a cylinder block of an internal combustion engine, a cylinder head gasket is situated therebetween to seal combustion gas and liquid or the like.
As shown in FIG. 4, the cylinder head gasket is manufactured in accordance with shapes of engine members, such as a cylinder block and the like, and includes holes 2 for cylinder bores, liquid holes, such as water holes 3 and oil holes 4, and bolt holes 5. Also, various sealing means 31, 62 are formed for the respective holes for sealing.
In these sealing means, even though sealing is provided between the same engine members by the same gasket, required sealing abilities are extremely different depending on the holes to be sealed. Namely, while it is necessary to seal high temperature and high pressure combustion gases in the holes 2 for the cylinder bores, it is necessary to seal the relatively low temperature liquid in the liquid holes 3 and 4.
On the other hand, since it is required to reduce a weight of the engine and manufacturing cost, a type of the cylinder head gasket has been changed from a laminate type in which a large number of metal plates are laminated to a simple metal gasket, which is formed of one or two metal plates. Since the number of the constituent plates is reduced, materials which can be used for the plates are limited. Also, in order to make the engine smaller, an area which can be used for sealing means has been reduced.
Therefore, it is difficult to freely combine beads, grommets, shims or the like which can be used as sealing means, or to provide double sealing means as in the laminate type gasket in which a large number of plates are laminated. The kind and the number of sealing means are limited, so that the simplified sealing means has to be used.
Examples of conventional cylinder head gaskets are shown in FIGS. 4 to 6. In the cylinder head gasket 1X or 1Y, there is provided a single, narrow-width bead 31 in a circular arc form which can follow the change in the space well, and the bead 31 is protected by a grommet 61 formed by bending a part of a base plate 60X or 60Y so as to prevent the high temperature and high pressure combustion gas from contacting the bead 31. Also, a bead 62, or half-beads 63 and 73 are provided for sealing around the liquid holes 3 and 4.
However, in the conventional cylinder head gasket 1X or 1Y, the base plate 60X or 60Y which contacts the engine member and the grommet 61 surrounding a periphery of the hole 2 for the cylinder bore, are formed of one plate. Namely, the grommet 61 is formed of the same material as that of the base plate 60X or 60Y.
On the other hand, since the grommet 61 is formed by bending the plate, it is preferable to use an annealed material, which does not crack in the bending process and is easy to deform, as a material of the grommet 61. On the other hand, in order to provide the bead 62 or the half beads 63 and 73, it is preferable to use a spring material as the material of the base plate.
Therefore, in case the grommet and the base plate are formed of the same material, it is difficult to satisfy both characteristics in one plate. Namely, the spring ability is required for the base plate, and the bending ability and heat resistance are required for the grommet liable to have the crack in the bent portion. It is difficult to obtain enough durability in one plate.
The present invention has been made to solve the foregoing problems, and an object of the invention is to provide a cylinder head gasket with a thin-plate structure, wherein a grommet formed of an optimum material can be provided around the hole for a cylinder bore while a base plate formed of an optimum material can be provided between a cylinder head and a cylinder block, so that the cylinder head gasket has a good sealing ability and an excellent durability.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the aforementioned object, the present invention provides a cylinder head gasket for sealing between a cylinder head and a cylinder block of an engine, in which a base plate forming the cylinder head gasket is formed of a first metallic material, and a peripheral member around a hole for a cylinder bore is formed of a second metallic material. The first metallic material is different from the second metallic material, and the peripheral member is connected to the base plate by welding.
According to this structure, since the peripheral member around the hole for the cylinder bore and the base plate are formed of different metallic materials, the peripheral member and the base plate can be respectively formed of suitable materials while a number of the base plates is small. Therefore, there can be obtained a light-weight cylinder head gasket with a thin-plate structure, which has a good sealing ability and an excellent durability.
Also, the present invention provides a cylinder head gasket, in which a grommet is formed around the hole for the cylinder bore, and the base plate is formed of a first metallic material. The grommet is formed of a second metallic material, which is different from the first metallic material. Also, the grommet is connected to the base plate by welding.
According to this structure, since the grommet and the base plate are formed of different metallic materials, the grommet and the base plate can be respectively formed of suitable materials. Thus, there can be obtained the cylinder head gasket which has a good sealing ability and an excellent durability.
Namely, a relatively low sealing surface pressure is sufficient in portions widely contacting engine members and portions for sealing a cooling water and a circulating oil around liquid holes, and these portions are mostly flat. Thus, it is preferable to use a material, such as spring material, having an adequate elasticity. On the other hand, around the holes for the cylinder bores, in order to seal the high pressure and high temperature combustion gas, it is necessary to have a high heat resistance, and a deformable characteristic is also required for the bending process. Thus, it is preferable to use a material, such as annealed material, which is excellent in the heat resistance and bending characteristic. By adopting the above structure of the invention, both the demands described above can be easily achieved.
Further, in the cylinder head gasket as stated above, the first metallic material forming the base plate is formed of a spring material, and the second metallic material forming the grommet is formed of an annealed material. The first metallic material forming the base plate can be a stainless steel plate, a spring material plate or the like, and the second metallic material forming the base plate forming the grommet can be an annealed stainless steel plate, a soft steel plate or the like. A combination of the spring plate and the annealed stainless steel plate is most preferable.
In the cylinder head gasket as stated above, spot welding portions are respectively formed in the base plate and the grommet, and spot weldings are applied at portions where the welding portions of the base plates and the grommet are overlapped, so that the grommet is integrally connected to the base plate.
According to this structure, since the grommet and the base plate are connected at the spot welding portions by welding, the portions where the grommet and the base plate are overlapped can be extremely small, so that a weight of the cylinder head gasket can be reduced and a material thereof can be saved.
In this case, it may be structured such that the end portions of the grommet and end portions of the base plate are overlapped in the circumferential areas, and the spot weldings are applied at several points of the overlapped portions. Alternatively, as in the cylinder head gasket used in a cylinder block of an open deck type, a space may be formed between the end portion of the grommet and the end portion of the base plate to obtain a passage for cooling water in a water jacket, and the overlapped portions are formed by the spot welding portions.
Incidentally, although a space between the grommet and the base plate can be welded throughout an entire periphery thereof, it is sufficient to handle the grommet and the base plate as an integral cylinder head gasket. Therefore, in view of reducing a number of working steps and weight of the gasket, it is preferable to connect the grommet and the base plate at the several points by spot welding.
Further, in the cylinder head gasket as stated above, a bead member may be disposed inside the grommet. According to this structure, the bead can be provided in the grommet, and by the elasticity of the bead, the excellent sealing ability can be exhibited. A material of the bead member can be a metallic material which is different from the metallic material of the base plate, or even if the material of the bead member is the same metallic material as that of the base plate, a thickness of the bead or heat history thereof can be changed.
Incidentally, although the aforementioned structures of the invention are especially effective in case a number of the base plate of the metal gasket is two, the same effects can be achieved even if the number of the base plate is one, or more than two including an intermediate plate. Also, a sectional shape and a size of the bead, and the material of the bead member can be adequately selected depending on the required sealing ability.